Repairing UV-Induced DNA Damage

An NIEHS grantee and colleagues report new details on how cellular machinery detects DNA damage caused by ultraviolet (UV) light and signals for repair. The new findings help explain why people with the inherited disease xeroderma pigmentosum are at an extremely high risk for developing skin cancer.

When DNA is damaged by UV light, a protein called human UV-damaged DNA-binding protein (UV-DDB) recognizes this damage and signals for a repair. To better understand how UV-DDB recognizes the damage, the researchers examined the process by tracking single molecules of UV-DDB tagged with light-emitting quantum dots. This let them watch the molecules move from place to place in real time on both normal and UV-exposed DNA strands.

The experiments revealed that UV-DDB stops along the DNA strand and transiently attaches to it, causing a change in the protein’s structure. If it comes to a spot damaged by UV radiation, two molecules of UV-DDB converge and stay bound to the site, signaling DNA repair machinery. The researchers also followed a quantum-dot labeled UV-DDB protein with a mutation associated with xeroderma pigmentosum. The mutant UV-DBB could still bind to DNA, but continued to slide along the DNA rather than remaining at the damaged site to signal that repair was needed.